This invention relates to an electron-beam shutter and a shutter tube incorporating an electron-beam shutter used in optoelectronic devices that record fast-transient luminous images.
To pick up any object that changes or vibrates at high speed, it is necessary to make the exposure time extremely short. In photographing, exposure is given by mechanical means. Meanwhile, optoelectronic image tubes convert images by use of the effect of photoelectric emission. In such an image tube, a fine-mesh electrode is provided close to, and parallel to, the photocathode. Usually, the electrode is held at a potential lower than that of the photocathode to prevent the passage of an electron-beam image. A potential higher than that of the photocathode is given to the electrode at a desired exposure time for a desired time length. Then, an electron-beam image, which corresponds to a luminous image projected on the photocathode, is passed to the fluorescent screen of the image tube at the desired time to reproduce the image of the original luminous event thereon, which is then recorded either on a photographic film or by use of a television camera.
In another type of image tube, there is provided, at a suitable point in the path of an electron-beam image between the photocathode and the fluorescent screen, a deflecting electrode which consists of two deflection plates disposed parallel to and on both sides of the path. Usually voltage is applied between the two deflection plates so that the electron-beam image does not reach the fluorescent screen. At a desired exposure time, the voltage applied between the two deflection plates is varied, whereby the electron-beam image, which corresponds to luminous image projected on the photocathode, reaches the fluorescent screen to reproduce the original image thereon when the voltage between the two deflection plates becomes small enough.
The image tubes having the above-described functions are called shutter tubes and used for the observation and analysis of such fast-transient events as spark discharge, explosion, combustion in the internal combustion engine, and impulse wave.
The same functions as above can be attained by providing a fine-mesh or deflecting electrode in the image section of such television cameras as an image orthicon and a silicon intensifier target vidicon, too.
The optoelectronic devices to record luminous images changing at high speed must be controlled to that only such electron beams are passed to the fluorescent screen or storage target as are emitted from the photocathode in such an extra-short time as several nanoseconds or even shorter. Namely, the electron-beam shutter must operate in such an extra-short time. As will be discussed at length later, however, the conventional electron-beam shutters have been unable to provide high enough shutter speeds to catch fast-transient luminous images.
An electron-beam shutter tube having a focusing electrode has the problem of applying high accelerating voltage on photoelectrons because of the great distance between the photocathode and fluorescent screen. The shutter tube of this type is large in size for the same reason. To operate the shutter properly, therefore, high shutter voltage must be applied on the fine-mesh or deflecting electrode.
In an electron-beam shutter tube consisting of a proximity type image tube without a focusing electrode but having a fine-mesh electrode too, high shutter voltage must be applied.